Data collection, such as for electric, gas, water and other utilities can be a costly and time-consuming process if performed manually. As a result, various technologies have developed to automatically gather utility consumption data using wired or wireless techniques, including automatic meter reading (AMR) systems. U.S. Pat. Nos. 5,581,229, 6,154,488 and 6,501,785, as well as published U.S. Patent Application Nos. 2002/0071478 and 2002/0109607, describe some of these systems.
Under the '0071478 application (and associated system manufactured by Itron, Inc. of Spokane, Wash.), a radio system at a meter or collection endpoint transmits eight identical packets on eight different frequencies, with a predetermined time interval between transmissions, depending upon a type of encoder receiver/transmitter (ERT). Thereafter a ten second delay is imposed, and the process repeats on eight new frequencies.
Each packet includes a preamble containing a number such as a hexadecimal number, a pseudo-random number (PN), or the like. Each packet is Manchester encoded, such that a one is represented by the bit sequence 10, while a zero is represented by the sequence 01. A reader samples a received signal at a known bit rate (e.g., a center two-thirds of each bit), and by comparing a relative difference between adjacent bits it determines a resulting bit stream, regardless of the noise floor. A correlator employed in a digital signal processor (DSP) looks for the preamble at a particular frequency, where the correlator time shifts received signals to search for a correlation. If a match is received, a distinctive signal pattern results. The system then determines whether a packet is bad based on a trailing cyclic redundancy check (CRC).
Under the '0109607 application, a powerful encoder transmitter (PET) system employs orthogonal frequency hopping tables to distinguish between endpoint nodes (e.g., meters or data collection devices). In other words, the hopping tables are not a subset pattern of each other. Under the orthogonal frequency hopping tables, each of the endpoints or transmitters under the PET system has a different pattern of hopping between the frequencies. This system provides a way to work within the guidelines of the Federal Communications Commission (FCC) Part 15.247, which requires a manufacturer who wants to increase transmit power to correspondingly require the receiver to track the frequency of the transmitter. (This rule prohibits a manufacturer from simply increasing transmit power, and distributing inexpensive receivers that simply pick up any signal on any channel.)
In the drawings, the same reference numbers identify identical or substantially similar elements or acts. To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the Figure number in which that element is first introduced (e.g., element 504 is first introduced and discussed with respect to FIG. 5).
The headings provided herein are for convenience only and do not necessarily affect the scope or meaning of the claimed invention.